Lignosulfonate treated fertilizer particles

ABSTRACT

Synthetic inorganic chemical fertilizers are treated with lignosulfonate to harden and provide anti-caking and anti-dusting properties to the fertilizer particles. The fertilizer/lignosulfonate mixture includes up to about 5.0% by weight lignosulfonate on fertilizer. An improved method of treating inorganic fertilizers with lignosulfonate is also disclosed.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.07/024,044 filed Mar. 10, 1987, now U.S. Pat. No. 4,846,871, July 11,1989.

BACKGROUND OF THE INVENTION

The present invention relates to fertilizers, and more particularly toinorganic chemical fertilizers treated with lignosulfonate to harden andgive anti-caking and anti-dusting properties to fertilizer particles.

Synthetic chemical inorganic fertilizers such as ammonium phosphates,ammonium nitrates, potassium nitrates, potassium chlorides, potassiumsulfates, calcium phosphates and many others are well known fertilizers.Methods of manufacturing these inorganic fertilizers as well as methodsof processing the fertilizers into particles via prill and/orgranulation techniques are also well known. The resulting fertilizerparticles, however, exhibit several undesirable characteristics. First,such particles tend to cake when stored and transported in bulk suchthat the initial free flowing particles change to a solid, substantiallyintegral mass. Secondly, such particles easily break into smallerparticles resulting in a substantial amount of dust being created whenhandled, transported and when eventually applied to the soil.

In order to overcome the above disadvantages, the prior art has taught anumber of conditioning agents which may be added to the fertilizerduring processing to harden and give anti-caking and anti-dustingproperties to fertilizer particles. For example, anti-caking propertieshave been imparted to fertilizer particles by utilizing clay, talc,surfactants, or a combination of these three conditioners, to coat theparticles. Additionally, various oils are sprayed on the particles forcontrolling dust. Also, a phosphoric acid-boric acid compound knownunder the trademark "PERMALENE" and available from Mississippi Chemical,has been utilized in phosphate production as a hardening agent.

It is also known to add 0.1% to 0.5% by weight of formaldehyde to ureaduring urea manufacturing to overcome the above noted disadvantages. Thefollowing patents discuss the reaction of formaldehyde with urea to formurea-formaldehyde products: U.S. Pat. Nos. 3,112,343; 4,160,782; and4,204,053. Health and safety considerations, however, have severelylimited the use of formaldehyde in fertilizer products, and in factformaldehyde is not widely accepted for use as a conditioning agent inthe preparation of urea or other fertilizers. Urea has also been treatedwith 0.1% to 5% by weight of lignosulfonates as shown in U.S. Pat. No.4,587,358. It is not, however, known heretofore to utilizelignosulfonate with other synthetic inorganic chemical fertilizers.

SUMMARY OF THE INVENTION

A synthetic inorganic chemical fertilizer selected from the groupconsisting of ammonium phosphates, ammonium nitrates, potassiumnitrates, potassium chlorides, potassium sulfates, calcium phosphatesand mixtures thereof, is treated with a lignosulfonate to harden thefertilizer particles and give anti-caking and anti-dusting properties tothe fertilizer. The lignosulfonate may be utilized with variousinorganic fertilizers and may be incorporated into various fertilizermanufacturing processes such as granulation and crystallization, i.e.prill, systems to impart the above advantageous properties tofertilizers produced in solid particulate forms, for direct applicationto soil.

The addition of lignosulfonate to the above noted inorganic fertilizersresults in harder particles less susceptible to breakage and formationof fines, and gives anti-caking and anti-dusting properties in one stepwithout the need for any secondary or additional conditioners. Thesubstitution of lignosulfonates for materials such as formaldehyde notonly reduces the cost of the fertilizer product, but also eliminates anyhealth and safety considerations in that lignosulfonates are approvedfor use as additives in animal feed products.

The fertilizer manufacturing process may incorporate up to about 5.0% byweight lignosulfonate with about 0.05% to about 0.7% preferred. Belowthese preferred levels, hardness is lowered due to insufficientlignosulfonate for binding while above the preferred dosage, hardness islowered presumably through a diluant effect.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In preparing the lignosulfonate treated fertilizer of the presentinvention, the first step is to select a desired lignosulfonate andhomogeneously mix the lignosulfonate with an inorganic fertilizer duringfertilizer production. Up to about 5.0% by weight lignosulfonate may beadded to the fertilizer with about 0.05% to about 0.7% preferred. 0.05%is the preferred practical lower limit since below this dosage, there isan inadequate hardness increase due to insufficient lignosulfonate forbinding, and 0.7% is believed to be the practical upper limit sinceabove this dosage hardness once again decreases which is presumably dueto a diluent effect.

As used herein, the term "fertilizer" is used in its broad, generalsense to mean a substance that is used to supply minerals to both plantsand animals. Therefore, fertilizers include substances used to make soilmore fertile as well as substances used as mineral supplements in animalfeeds. The synthetic inorganic chemical fertilizers utilized in thepresent invention may be selected from the commonly known fertilizersconsisting of ammonium phosphates, ammonium nitrates, potassiumnitrates, potassium chlorides, potassium sulfates, calcium phosphates,and mixtures thereof. All of the above fertilizers as well as theirmethods of production are commonly known and need not be described indetail herein.

As used herein, the term "Kraft lignin" has its normal connotation, andrefers to the substance which is typically recovered from alkalinepulping black liquors, such as are produced in the Kraft, soda and otherwell known alkaline pulping operations. The term "sulfonated lignin", asused in the specification, refers to the product which is obtained bythe introduction of sulfonic acid groups into the Kraft lignin molecule,as may be accomplished by reaction of the Kraft lignin with sulfite orbisulfite compounds, so that Kraft lignin is rendered soluble in water.As used herein, the term "sulfite lignin" refers to the reaction productof lignin which is inherently obtained during the sulfite pulping ofwood, and is a principle constituent of spent sulfite liquor. The term"lignosulfonate" (LS)₃) encompasses not only the sulfite lignin, butalso the sulfonated lignin herein above described. Any type oflignosulfonate i.e. hardwood, softwood, crude or pure may be employed.For example, calcium lignosulfonates, sodium lignosulfonates, ammoniumlignosulfonates, modified lignosulfonates, and mixtures or blendsthereof may all be utilized herein. Lignosulfonates are available fromnumerous sources, in either aqueous solution or dried powder forms. Forexample, Daishowa Chemicals Inc. sells lignosulfonates under the tradedesignations "Lignosol" and "Norlig HP" which are appropriate for use inthe present invention.

In present fertilizer prill production, a fertilizer generally at 70%solids concentration in water is heated in evaporators to about 285° F.to remove substantially all the water. The molten fertilizer is theninjected as droplets to an air cooling tower where crystallinefertilizer is formed as a hard prill or bead used for shipment. With thepresent process, up to about 5.0% by weight lignosulfonate may be addedto the 70% fertilizer solution prior to heating with 0.05% to 0.7%preferred. With loading over 0.7% hardness decreases presumably througha diluant effect, and with loading under 0.05% insufficientlignosulfonate is present for binding. The lignosulfonate is soluble inthe molten fertilizer and solidifies with the fertilizer when cooled inthe air cooling tower. The lignosulfonate is the ingredient thatprovides the desired advantages for the fertilizer and once the moltenfertilizer and lignosulfonate are crystallized it is believed that thelignosulfonate serves to encase or entrap the fertilizer to harden andgive anti-caking and anti-dusting properties to the fertilizerparticles. Examples are shown herein where fertilizer strength has beenincreased from about 180 psi to about 780 psi depending uponlignosulfonate dosage. Lignosulfonate in either powder or liquid formmay be utilized.

The following examples are given as being illustrative of the advantagesof the present invention.

EXAMPLE I

0.4% by weight Norlig HP was added to an 83% ammonium nitrate solutionat elevated temperature to form a homogeneous solution. This solutionwas then evaporated to 98+% molten ammonium nitrate and formed intoplates and crystallized. Hardness of the crystal plate was measured withan ACME penetrometer and calculated to pounds per square inch resistanceto breakage. The pressure shown below is the average of four platemeasurements.

    ______________________________________                                                          Lbs. Pressure                                                                          Calc.                                                                for Breakage                                                                           PSI                                                ______________________________________                                        Ammonium Nitrates Crystal Plate                                                                   116        4646                                           No Additive                                                                   Ammonium Nitrate Crystal Plate                                                                    172        6880                                           0.4% Norlig HP Additive                                                       ______________________________________                                    

The above data clearly indicates that the addition of lignosulfonate toammonium nitrate yielded a crushing strength or hardness that was muchgreater than untreated ammonium nitrate. In fact, the above exampleshowed a 48% increase in strength.

EXAMPLE II

Ground monoammonium phosphate (MAP) (16-200+Mesh) was stirred with 30%water containing lignosulfonate and oven dried at 105° C. The resultingthin sheets of MAP representing granule formation were crushed using anACME penetrometer. Results are shown below and indicate 0.4% oflignosulfonate (Norlig A) more than doubled the crushing strength ofMAP.

    ______________________________________                                        HARDENER FOR MONOAMMONIUM PHOSPHATE                                           Norlig A     Crushing Strength                                                %            psi                                                              ______________________________________                                        0            280                                                              0.2          510                                                              0.4          600                                                              1.0          520                                                              ______________________________________                                    

EXAMPLE III

Norlig HP (low foam) was added to diammonium phosphate (DAP) and the mixdried as would occur in a commercial granulation procedure. DAP plateswere formed and tested for hardness using an ACME penetrometer. Resultswere as follows:

    ______________________________________                                        % Norlig     Hardening (psi,                                                  HP Solids    ACME Penetrometer)                                               ______________________________________                                        0            180                                                              0.2          390                                                              0.4          320                                                              0.6          780                                                              0.8          500                                                              1.0          340                                                              ______________________________________                                    

These results indicate an optimum dosage of approximately 0.05% to 0.7%Norlig HP solids on DAP. Below that, hardness is lowered due toinsufficient product for binding. Above that dosage, hardness is loweredpresumably through a diluant effect. Visual observation noted that theincorporation of Norlig HP into DAP exhibited anti-caking andanti-dusting properties as well as hardening.

EXAMPLE IV

A modified lignosulfonate was added to potassium nitrate, potassiumchloride and potassium sulfate, and test plates were prepared as inExample III. Results were as follows:

    ______________________________________                                                       HARDNESS                                                                            ACME                                                                          Penetrometer                                                                             %                                             Product   % LSO.sub.3                                                                              (psi)      Increase                                      ______________________________________                                        Potassium 0           20        --                                            Nitrate   5.0        140        700                                           Potassium 0           40        --                                            Chloride  5.0        230        575                                           Potassium 0           50        --                                            Sulfate   5.0        490        880                                           ______________________________________                                    

The results indicate that up to 5.0% by weight modified lignosulfonatemay be utilized to increase hardness of inorganic fertilizers.

EXAMPLE V

In a typical process for making dicalcium phosphate, a slurry of 400mesh limestone and concentrated phosphoric acid is fed into a pug millto produce approximately 24 tons/hr. of rough product. In the case ofmonocalcium phosphate, additional dry limestone is also added to themill.

In both cases, about 100 tons/hr. of recycle material (fines, includingcrushed oversized, and product) is also fed into the mill. Thesevariables together give a moisture content in the mill of 5-7%. From thepug mill, rough product is fed into a cocurrent drum dryer. Residencetime in the dryer is about 12 minutes. From the dryer, the still roughproduct is sent to an elevator for transfer to the screen room. Herefines (-65 mesh) and oversize (+14 mesh) are removed and final product,less recycle, is sent to storage.

Approximately 0.25% by weight Norlig HP 1 was sprayed into the end ofthe pug mill during a dicalcium phosphate run. Samples of the resultingproduct were taken at approximately 20 and 40 minutes into the run. Theresults of the analysis of these samples are indicated below. Asignificant decrease in fines was observed in both samples. The amountof 65 mesh material was also less. Overall, the amount of final productpresent in the samples was up and the distribution of material withinthe allowable range was improved.

    ______________________________________                                        Wt % Retained on Screen                                                                      HP 1 Spray Treated                                             Mesh Size Control    20 Minutes                                                                              40 Minutes                                     ______________________________________                                        14        11.9       10.7       9.9                                           12         3.4        3.0       3.3                                           20        10.0        8.7      10.3                                           28        19.6       20.2      22.5                                           42        32.6       37.0      35.7                                           65        16.1       15.4      12.5                                           -65        6.4        5.0       5.2                                           ______________________________________                                    

EXAMPLE VI

A second trial in a dicalcium phosphate process as described in ExampleV was performed utilizing a dosage of about 0.1% by weight Norlig HP 1sprayed onto the product. Spraying began at 10:30 a.m. and samples wereanalyzed at 11:00 a.m., 12:00 noon and 1:00 p.m. The results are shownbelow

    ______________________________________                                        Screen Mesh   Wt % Retained                                                   ______________________________________                                        Control Data                                                                  12            21.4                                                            14             4.4                                                            20            11.2                                                            28            22.2                                                            42            22.8                                                            65            12.5                                                            -65            5.5                                                            11:00 A.M. Data                                                               12            22.6                                                            14             4.1                                                            20             8.7                                                            28            18.2                                                            42            30.0                                                            65            11.9                                                            -65            4.5                                                            12:00 Noon Data                                                               12            19.1                                                            14             4.3                                                            20             9.9                                                            28            20.7                                                            42            32.6                                                            65            10.0                                                            -65            3.4                                                            1:00 P.M. Data                                                                12            17.1                                                            14             4.1                                                            20            10.8                                                            28            23.3                                                            42            31.4                                                            65            10.0                                                            -65            3.3                                                            ______________________________________                                    

After 30 minutes, the 11:00 a.m. data showed an immediate reduction infines in the unscreened product from 5.5% to 4.5%. The 12:00 noon sampleshowed a further decrease in the amount of fines in the unscreenedproduct (down to 3.4%). In addition to this, a decrease in the amount ofoversize material was also observed (from 22.6% to 19.1%). The 1:00 p.m.sample showed that the amount of fines was down to 3.3% and the amountof oversize was down an additional 2% to 17.1%. In summary, the datashows that during spray treatment with 0.1% Norlig HP 1:

(1) fines were down some 40% (from 5.5 to 3.3%)

(2) oversize was down some 20% (from 21.4 to 17.1%)

(3) product (i.e. -14-+65 mesh material) was up about 9% (from 73.1 to79.6%); it appears from the data that most of the increase is in the-28-+42 mesh range.

At 1:00 p.m. the dosage was increased to 0.16% Norlig HP 1.Unfortunately, the plant was forced to shut down shortly thereafter, andthis trial was ended. Before the trial ended, however, a sample of thefinal product was obtained, and the results of the analysis of thissample are shown below.

Results of Final Product Screen Analysis

    ______________________________________                                        Results of Final Product Screen Analysis                                      DiCal Trial Spray                                                             Screen Mesh                                                                             Cummulative % Retained                                                                          Wt % Retained                                     ______________________________________                                        12        12.5              12.5                                              14        48.7              36.2                                              20        78.4              29.7                                              28        96.9              18.5                                              42        99.89             2.99                                              65        99.95             0.06                                              -65       100.00            0.05                                              ______________________________________                                    

EXAMPLE VII

Another trial in the dicalcium phosphate (DAP) process as described inExample V was performed utilizing dosages of about 0.069% and 0.15% byweight Norlig HP 1 sprayed onto the product. The crush strength andattrition (break-up to fines) evaluations are shown below.

    __________________________________________________________________________    DAP TEST RESULTS                                                              Sample                                                                              HP-1 DOSAGE                                                                            % HP Solids on                                                                        Crush %    %                                           No.   (gals/ton)                                                                             DAP Solids                                                                            Strength %                                                                          Attrition                                                                          Lower Fines                                 __________________________________________________________________________    R-192-3                                                                             0        --      431   1.56 --                                          Control-Oil                                                                   R-192-1                                                                             0.25     0.069   596   0.56 64                                          (Norlig)                                                                      R-192-2                                                                             0.57     0.157   480   0.66 58                                          (Norlig)                                                                      __________________________________________________________________________

The results indicate that the usage of very small amounts, even aslittle as 0.05% by weight lignosulfonate, may be utilized to increasehardness of inorganic fertilizers.

The following procedure is utilized in obtaining the hardness orcrushing strength data referred to above and reported in Examples Ithrough VII. In this procedure the fertilizer being tested is melted,slurried or dissolved in a small metal dish. A predetermined amount ofconditioner or lignosulfonate e.g. Norlig HP, is added and the two arethoroughly mixed to form a consistent mixture or solution. The system isthen cooled and dried, giving crystal plates or granules suitable forcrushing. These plate or granule segments are crushed using an ACMEpenetrometer to obtain a measure of the relative crushing strength ofthe various conditioners. The penetrometer is used with a 0.1 in.² areaspindle. Pounds of force are read from a gauge. Pounds per square inchcrushing strength is calculated by multiplying the force figure times10. In the screening test, visual observation is employed to determinewhether a conditioner that increases granule or plate hardness alsoimparts anti-caking and anti-dusting properties. More accurateanti-caking and anti-dusting evaluations may be performed separately bylong-term storage or accelerated storage tests.

It is clear from the above Examples that the hardness as well as theanti-caking and anti-dusting properties of synthetic inorganic chemicalfertilizers has increased dramatically when a lignosulfonate is employedtherewith.

The lignosulfonate that provides the advantageous properties of thepresent invention may also be utilized with ammonium nitrate, potassiumnitrate, potassium sulfate, potassium chloride, ammonium phosphate andcalcium phosphate fertilizers produced in solid particulate form byconventional granulation methods.

For example, when conventionally producing granular ammonium phosphate,phosphoric acid is neutralized with ammonia in a series of ammoniationreaction tanks where the heat of reaction evaporates a part of the waterintroduced with the acid. The extent of ammoniation is controlled toyield a slurry composition ranging from monoammonium phosphate to abouttwo-thirds diammonium phosphate, depending on the grade of productdesired. This slurry flows to a pugmill or blunger in which it isgranulated by mixing with recycled product fines. The granules are thendried and screened to provide a product fraction and a finer recyclefraction. Recycle ratios in the order of 8:1 are required for propercontrol of granulation. In one variation of the process, a rotary drumgranulator is substituted for the blunger. Products made in this mannercontain 11% N and 21% P, predominantly monoammonium phosphate; and 16% Nand 21% P, about one-third monoammonium and two-thirds diammoniumphosphate. Other grades such as one containing 16% N and 8.7% P andanother with 13% N and 17% P may be made by adding sulfuric acid to theammoniators, in which case the product contains ammonium sulfate. Instill another variation, unfiltered extract from a phosphoric acid plantis used to produce lower grades that contain calcium sulfate.

Diammonium phosphate containing 18% N and 20.1% P is also made by aprocess in which phosphoric acid is neutralized with ammonia in a rotarydrum granulator. Heated air and dry recycled fines are introduced in thegranulator to reduce the moisture content to the proper level forgranulation. The gases leaving the granulator are scrubbed with theincoming acid. The product is dried and then screened.

An alternate process for a material containing 18% N and 20.1% P alsouses a rotary granulation drum. Phosphoric acid is neutralized in aprereactor with anhydrous ammonia to an NH₃ :H₃ PO₄ mole ratio of about1.3, a point near the maximum solubility of the system. The slurry thusproduced is fed to the granulator along with recycled fines. Additionalammonia is added in the granulation step to give a mole ratio of about2, a point of minimum solubility. The excess ammonia required to drivethe reaction to diammonium phosphate is recovered by scrubbing theexhaust gases with the incoming acid before it is fed to the prereactor.The product from the granulator is dried and screened. In addition tothe material containing 18% N and 20.1% P, a large variety of gradesrich in diammonium phosphate can be conventionally produced byneutralizing with ammonia-ammonium nitrate solutions rather thananhydrous ammonia, substituting sulfuric acid for part of the phosphoricacid, or adding various solid fertilizer ingredients to the ammoniator.

Ammonium nitrate may be conventionally produced in granular formsubstantially as described by the above processes by initially startingwith the neutralization of nitric acid with ammonia in the ammoniationreaction tanks. Similarly, potassium nitrate may be conventionallyproduced in granular form from potassium chloride and sodium nitratewhile ammonium phosphate may be conventionally produced in granular formfrom ammonia and phosphoric acid.

Calcium phosphates are conventionally produced in numerous well knownmethods. For example, dicalcium phosphate is prepared from calciumchloride (CaCl₂) and disodium phosphate (Na₂ HPO₄).

In any of the above fertilizer granulation processes, up to about 5.0%lignosulfonate by weight may be added to the fertilizer, and it ispreferred to add 0.05% to 0.7% by weight lignosulfonate in thegranulation process. The lignosulfonate in either liquid or solid formmay be incorporated in the granulation process in the reaction tanks, inthe recycled fines, or directly in the granulators. Preferably, thelignosulfonate is incorporated in the recycled fines and is sprayed ontothe particles within the granulators where it aids in building the sizeof the granules being formed therein. The hardness of the resultantfertilizer granules is increased to thus provide stronger fertilizergranules having improved anti-caking and anti-dusting properties.

Various modes of carrying out the invention are contemplated as beingwithin the scope of the following claims particularly pointing out anddistinctly claiming the subject matter regarded as the invention.

I claim:
 1. A composition of matter, consisting essentially of anadmixture of a fertilizer selected from the group consisting of ammoniumnitrate, ammonium phosphate, potassium nitrate, potassium sulfate,potassium chloride, calcium phosphate and mixtures thereof, and from0.05% up to about 5.0% by weight of a lignosulfonate such that thehardness anti-caking and anti-dusting properties of the fertilizer areincreased.
 2. The composition of claim 1 wherein said lignosulfonatecomprises about 0.05% to about 0.7% by weight of said admixture.
 3. Thecomposition of claim 1 wherein said lignosulfonate is selected from thegroup consisting of sulfite lignin and sulfonated lignin.
 4. Thecomposition of claim 1 wherein said lignosulfonate is obtained from thepulping of hardwoods.
 5. The composition of claim 1 wherein saidlignosulfonate is obtained from the pulping of softwoods.
 6. A method oftreating a fertilizer to improve the fertilizer's hardness, anti-cakingand anti-dusting properties, consisting essentially of the stepsof:preparing an admixture of from 0.05% up to about 5.0% by weight of alignosulfonate and a fertilizer selected from the group consisting ofammonium nitrate, ammonium phosphate, potassium nitrate, potassiumsulfate, potassium chloride, calcium phosphate and mixtures thereof; andprocessing said admixture into a particulate form.
 7. The method ofclaim 6 wherein said step of processing involves producing granules andsaid lignosulfonate is sprayed onto the fertilizer.
 8. The method ofclaim 6 wherein said step of processing involves producing prill andsaid lignosulfonate is mixed with molten fertilizer prior to cooling. 9.The method of claim 6 wherein said lignosulfonate comprises from about0.05% to about 0.7% by weight of the admixture.
 10. The method of claim6 further including the step of selecting a lignosulfonate from either asulfite lignin or sulfonated lignin prior to preparing the admixture.11. The method of claim 10 wherein said lignosulfonate is obtained fromthe pulping of hardwoods.
 12. The method of claim 10 wherein saidlignosulfonate is obtained from the pulping of softwoods.